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Altered brain concentrations of citalopram and escitalopram in P-glycoprotein deficient mice after acute and chronic treatment
Linköping University, Department of Medical and Health Sciences, Clinical Pharmacology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medical and Health Sciences, Clinical Pharmacology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Pharmacology.
Department of Psychiatry and Psychotherapy, University Medical Center of the Johannes Gutenberg-University of Mainz, Mainz, Germany.
Linköping University, Department of Medical and Health Sciences, Clinical Pharmacology. Linköping University, Faculty of Health Sciences.
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2013 (English)In: European Neuropsychopharmacology, ISSN 0924-977X, E-ISSN 1873-7862, Vol. 23, no 11, 1636-1644 p.Article in journal (Refereed) Published
Abstract [en]

Background: According to both in vitro and in vivo data P-glycoprotein (P-gp) may restrict the uptake of several antidepressants into the brain, thus contributing to the poor success rate of current antidepressant therapies. The therapeutic activity of citalopram resides in the Senantiomer, whereas the R-enantiomer is practically devoid of serotonin reuptake potency. To date, no in vivo data are available that address whether the enantiomers of citalopram and its metabolites are substrates of P-gp.

Methods: P-gp knockout (abcb1ab (-/-)) and wild-type (abcb1ab (+/+)) mice underwent acute (single-dose) and chronic (two daily doses for 10 days) treatment with citalopram (10 mg/kg) or escitalopram (5 mg/kg). Serum and brain samples were collected 1-6 h after the first or last i.p. injection for subsequent drug analysis by an enantioselective HPLC method. Results: In brain, 3-fold higher concentrations of S- and R-citalopram, and its metabolites, were found in abcb1ab (-/-) mice than in abcb1ab (+/+) mice after both acute and chronic citalopram treatments. After escitalopram treatment, the S-citalopram brain concentration was 3-5 times higher in the knockout mice than in controls.

Conclusions: The results provide novel evidence that the enantiomers of citalopram are substrates of P-gp. Possible clinical and toxicological implications of this finding need to be further elucidated.

Place, publisher, year, edition, pages
Elsevier, 2013. Vol. 23, no 11, 1636-1644 p.
Keyword [en]
Citalopram, enantiomers, escitalopram, mice knockout, P-glycoprotein
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-76122DOI: 10.1016/j.euroneuro.2013.01.003ISI: 000328014700033OAI: diva2:512530
Available from: 2012-03-28 Created: 2012-03-28 Last updated: 2014-01-08Bibliographically approved
In thesis
1. P-glycoprotein and chiral antidepressant drugs: Pharmacokinetic, pharmacogenetic and toxicological aspects
Open this publication in new window or tab >>P-glycoprotein and chiral antidepressant drugs: Pharmacokinetic, pharmacogenetic and toxicological aspects
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The blood-brain barrier (BBB) is formed by the capillary endothelial cells, joined together by tight junctions, with transporter proteins. BBB acts to regulate the brain concentrations of substances including many drugs. Transport across the cells is necessary for a drug to ensure that the drug reaches the site of action and transport proteins such as P-glycoprotein (P-gp; ABCB1) can limit the entrance into various tissues, including the brain.

Molecules that are not superimposable on their mirror images and thus exist in two enantiomeric forms (enantiomers) are said to be chiral. A racemic compound is one composed of a 50:50 mixture of two enantiomers, S- and R-enantiomers. Two examples of frequently prescribed racemic drugs are the chiral antidepressants venlafaxine (VEN) and citalopram (CIT). The enantiomers of VEN possess different pharmacodynamic profiles where the R-enantiomer is a potent inhibitor of both serotonin and noradrenaline reuptake (SNRI), while the S-enantiomer is more selective in inhibiting serotonin reuptake (SSRI). The SSRI effect of CIT resides in the S-enantiomer, whereas the R-enantiomer is considered to be therapeutically inactive, or even that it counteracts the effects. The S-enantiomer of CIT is now available as a separate SSRI (escitalopram, EsCIT). VEN and CIT are also among the most commonly found drugs in forensic autopsy cases.

Few previous studies have examined a possible enantioselective activity of P-gp. Thus, the general aim of this thesis was to study the enantiomeric distribution of chiral antidepressant drugs, focusing on the role of P-gp in the BBB. For this purpose, a mouse model disrupted of the genes coding for P-gp (abcb1ab (-/-) mice) was used. Brain and serum concentrations of the enantiomers of VEN and CIT, and their major metabolites, were compared to the corresponding wild-type mice (abcb1ab (+/+) mice). The open-field locomotor and rearing activities were examined after chronic VEN administration. In addition to the animal studies, genetic and toxicological aspects of P-gp were studied in a forensic autopsy material, where intoxication cases were compared with cases that were not related to intoxications.

The brain to serum concentration ratios for VEN, CIT and EsCIT differed between knockout mice and wild-type mice, with 2-3 fold higher brain concentrations in mice with no expression of P-gp. Hence, all studied drugs, and their major metabolites, were substrates for P-gp. There was no evidence for a stereoselective P-gp mediated transport. The P-gp substrate properties were reflected in the open-field behavior test where the knockout mice displayed increased center activity compared with wild-type mice following chronic VEN exposure. The genotype distribution of ABCB1 SNPs C1236T, G2677T and C3435T in VEN positive cases was significantly (or borderline) different between the intoxication cases and the non-intoxication cases. This difference in genotype distribution was not observed for the CIT positive cases.

To conclude, the present work has led to an increased knowledge about how the enantiomers of VEN and CIT are affected by the BBB transporter P-gp. Using an animal model, VEN and CIT have proved to be actively transported out of the brain by P-gp and no difference was observed for the enantiomers with regard to P-gp transport. Further, the ABCB1 genotype distribution was different in intoxication cases compared with non-intoxication cases. Taken together, these findings offer the possibility that the expression of P-gp in humans may be a contributing factor for limited treatment response and increased risk of side-effects following antidepressant drug treatment.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 80 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1283
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-76126 (URN)978-91-7393-003-1 (ISBN)
Public defence
2012-04-13, Berzeliussalen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Available from: 2012-03-28 Created: 2012-03-28 Last updated: 2012-03-28Bibliographically approved

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